I’ve had several ideas for a tale in Bellerverse, but I can’t get a storyline of some sort out together. I’ve had ideas for trying to incorporate SCP-085 (Cassie) into the canon, or one of the memetic SCPs. Maybe something to do with Clef or Bright since they’re not really featured a lot? But I can’t think of one solid story for it, just a mishmash of ideas that I think would be interesting.
Does anyone have any tips on brainstorming, or anything of the sort?

I’ve had ideas for trying to incorporate SCP-085 (Cassie) into the canon, or one of the memetic SCPs.

Why Cassie? Why a memetic SCP? What kind of story would you be telling with those sorts of references?

Maybe something to do with Clef or Bright since they’re not really featured a lot?

Why? "They're not featured a lot" doesn't necessarily automatically translate to "they should be featured more". What role would either of these characters play in the Bellerverse?

But I can’t think of one solid story for it, just a mishmash of ideas that I think would be interesting.

Maybe focus on why you think those ideas are interesting on their own, and build on that to get to something that the audience can get excited about?

Does anyone have any tips on brainstorming, or anything of the sort?

Don't force connections just for the sake of having one large piece. If possible, keep your premise simple. It's totally fine to let something sit and simmer for a bit while you think up some stronger narrative premises besides "I think it would be a good idea".